CONVECTIVE FORECAST
VALID 06Z THU 12/06 - 06Z FRI 13/06 2003
ISSUED: 12/06 02:16Z
FORECASTER: GROENEMEIJER

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND NORTHEASTERN FRANCE, THE SOUTHEASTERN BENELUX COUNTRIES AND PARTS OF WESTERN GERMANY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF FRANCE AND GERMANY AND THE SOUTHEASTERN BENELUX COUNTRIES AS WELL AS WESTERN PARTS OF THE CZECH REPUBLIC AND POLAND.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS A PART OF NORTHERN ITALY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS MUCH OF WESTERN CONTINENTAL EUROPE INCLUDING NORTHERN AND WESTERN PARTS OF IBERIA, CENTRAL AND SOUTH-CENTRAL EUROPE AND THE WESTERN BALKANS AS WELL AS A PART OF SOUTHERN SCANDINAVIA AND A PART OF THE UKRAINE AND RUSSIA.

SYNOPSIS

A SHORTWAVE TROUGH EMBEDDED IN A STRONG WSW-LY FLOW WILL TRACK ENE-WARD. A RIDGE FROM SOUTHWESTERN SCANDINAVIA INTO CENTRAL EUROPE WILL WEAKEN AS THE TROUGH APPROACHES. ANOTHER TROUGH IS PRESENT OVER WESTERN RUSSIA. QUIESCENT CONDITIONS PREVAIL OVER SOUTHERN EUROPE.

DISCUSSION

...WESTERN EUROPE...
A POORLY DEFINED FRONTAL ZONE IS ANALYSED FROM NEAR NANTES TO LUXEMBOURG AT 00Z. IN RESPONSE TO AN APPROACHING UPPER TROUGH, A FRONTAL WAVE IS EXPECTED TO DEVELOP OVER CENTRAL FRANCE DURING THE MORNING, SO THAT THE FRONTAL ZONE WILL MOVE SOMEWHAT FURTHER NORTH OVER EASTERN FRANCE, BENELUX AND GERMANY INITIALLY BEFORE RETREATING SOUTHWARD LATER ON THE DAY.

VERY HIGH LATENT INSTABILITY WILL FORM OVER CENTRAL, EAST-CENTRAL AND NORTHEASTERN FRANCE. INSPECTING NUMERICAL OUTPUT AND MODIFYING 00Z UPPER-AIR OBSERVATIONS LFLL, LFSN AND LFBD LEARNS THAT MLCAPE50 WILL LIKELY REACH AROUND 3000 J/KG IN PLACES WHEN EXPECTED DEW POINT TEMPERATURES OF 20-22C WILL BE PRESENT AND TEMPERATURES RISE QUICKLY ABOVE 30C. THOUGH QUITE SOME CONVECTIVE INHIBITION IS PRESENT IN THE BORDEAUX (LFBD) AND LSMP (PAYERNE) SOUNDINGS, LOCALLY THE INHIBITION SHOULD BE OVERCOME. ESPECIALLY ON THE EASTERN FLANK OF THE FRONTAL WAVE, WHERE SLIGHT WARM ADVECTION WILL LEAD TO RISING MOTIONS AND SUBSEQUENT DECREASE OF CONVECTIVE INHIBITION, STORM COVERAGE WILL BE HIGH.

WITHIN THE MDT RISK AREA, AND TO THE NORTH AND NORTHEAST OF IT, SHEAR WILL LIKELY BE MORE THAN ADEQUATE FOR SUPERCELL DEVELOPMENT. SOUTH OF THIS AREA, SOME SUPERCELLS MAY OCCUR, BUT MOST CONVECTION WILL BE MULTICELLS. EXPECT MANY OF THE STORMS TO BE ASSOCIATED WITH LARGE HAIL. DRY MID-LEVELS EVIDENT FROM UPPER-AIR SOUNDINGS WILL LIKELY AID IN THE FORMATION OF STRONG DOWNBURSTS. THE HAIL AND WIND THREAT WILL BE HIGHER WITH ANY SUPERCELL THAT FORMS AS THESE WILL LIKELY BE CAPABLE OF PRODUCING VERY LARGE HAIL / POSSIBLY LARGER THAN 5 CM IN DIAMETER / AND WIND GUSTS EXCEEDING 65 KNOTS. TORNADO THREAT SEEMS NOT TO BE PARTICULARLY HIGH SINCE LOW LEVEL SHEAR WILL BE LOW TO MODERATE AND LCL HEIGHTS ARE NOT EXPECTED TO BE PARTICULARLY LOW. HOWEVER, A FEW TORNADOES, THAT MAY POSSIBLY BE STRONG (F2 OR HIGHER) WILL BE POSSIBLE. MOST LIKELY LOCATION OF TORNADO DEVELOPMENT WILL BE NEAR THE FRONTAL ZONE, WHERE LCL HEIGHTS ARE THE LOWEST. ALSO, STORM COVERAGE WILL BE THE HIGHEST NEAR THE FRONTAL ZONE SO THAT CHANCES OF STORMS INTERACTING WITH BOUNDARIES FROM OTHER STORMS SEEMS TO BE THE HIGHEST THERE. IT IS NOT RULED OUT THAT ONE OR TWO NON SUPERCELLULAR TORNADOES /LANDSPOUTS/ WILL FORM FURTHER SOUTH AS THE PRESENCE OF SUBSTANTIAL LOW-LEVEL (0-3KM) CAPE WILL BE WILL ALLOW FOR STRETCHING OF PRE-EXISTING LOW-LEVEL VERTICAL VORTICITY.

NUMERICAL MODELS SUGGEST THAT A MCS MAY FORM WITHIN THE WARM ADVECTION REGIME EAST OF THE FRONTAL WAVE DURING THE AFTERNOON AS STORMS START TO CLUSTER. THE MCS, THAT WILL LIKELY CONTAIN A FEW SUPERCELLS, IS EXPECTED TO MOVE EASTWARD OVER CENTRAL AND/OR NORTHERN GERMANY DURING THE AFTERNOON AND EVENING. IT WILL LIKELY BE ELEVATED IN NATURE IN THE NORTH. THE MCS WILL POSE A THREAT OF LARGE HAIL, DAMAGING GUSTS AND FLASH FLOODING. A SMALL TORNADO THREAT WILL PERSIST UNTIL EARLY NIGHT ESPECIALLY WITH THE SOUTHERN PARTS OF THE SYSTEM.

...ITALY...
A QUIESCENT FLOW PATTERN IS IN PLACE OVER ITALY. SUBSIDENCE IN A HIGH PRESSURE SYSTEM OVER THE WESTERN MEDITERRANEAN HAS CAUSED SIGNIFICANT DRYING OF MID-LEVELS IN THE AREA. THIS CAUSES A THREAT OF VERY STRONG DOWNBURSTS WITH ANY STORM THAT FORMS. THERE IS ALSO A THREAT OF HAIL, THAT MAY REACH THE SEVERE LIMIT OF 2 CM IN SOME PLACES.

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